An optical network known as FTTP (“Fiber To The Premises”) or FTTH (“Fiber To The Home”) is an optical access network that supplies broadband or ultra-broadband communication services to a number of end users (e.g., services that require data transmission speeds measuring several hundred Mbit/s or even higher).
An optical FTTP or FTTH network typically includes a distribution box, which is typically located in the basement or vault of the building in which the end users reside. As used herein, a “riser cable” is an optical-fiber cable that typically leads out of the distribution box and runs in a vertical direction in the interior of the building from the basement or vault to each floor. Between two successive floors, the riser cable is typically laid in a duct, which mechanically protects the cable. This duct can be fixed to the surface of a wall or can be housed within the wall itself (e.g., in concrete). For example, the riser cable can run within this duct together with other cables, such as cables for distributing power and telephone cables.
At each floor of the building, the optical, electric, and telephone cables typically pass through junction boxes or cases so as to be connected to the equipment in the apartments or offices of the end users. A junction box typically has a minimum surface area of about 10 centimeters×10 centimeters.
The riser cable can be connected optically to one or more drop cables. As used herein, a “drop cable” is an optical-fiber cable that typically runs towards an apartment or office of an end user within a special duct fixed to the surface of the wall or housed within the thickness thereof. To connect the riser cable to the drop cables, a number of optical fibers are pulled out of the riser cable and are spliced to respective ends of the optical fibers of the drop cables. Each drop cable is then typically terminated in a termination box located in the proximity of or inside an apartment or office of an end user.
U.S. Patent Publication No. 2010/0232752, which is hereby incorporated by reference in its entirety, describes a branching device for a riser cable. A window is cut in the casing of the riser cable at a branching point thereof so as to expose the fibers enclosed therein. The branching device is positioned at the branching point and includes a housing for the riser cable and six outlet ports. The outlet ports branch off from the housing in an oblique direction. The outlet ports are suitable for conducting six fibers pulled out of the riser cable to the outside of the device such that they can be spliced to respective optical fibers of drop cables. Each splice is housed in a telescopic protection device, which is connected to the respective outlet port of the branching device. This telescopic protection device can be lengthened so as to house the excess length of the spliced fibers. The splice and the excess length housed in the telescopic protection device can be located in the duct in which the drop cable is laid. The telescopic protection device is made of flexible material and therefore can be rolled up within the duct, if required.
European Patent Publication No. 2,141,528, which is hereby incorporated by reference in its entirety, describes a modular distribution box that is suitable for receiving a riser cable and for distributing the fibers of the riser cable to a user. The box includes two stackable layers and a cover. The lower layer is substantially flat and has an inlet port and two outlet ports to allow the riser cable to pass through the box. The lower layer also has a routing element, which is suitable for routing the fibers pulled out of the riser cable from the lower layer to the upper layer. The upper layer includes reception channels that are suitable for receiving the fibers of the riser cable from the lower layer. Any splices between the fibers of the riser cable and the fibers of the drop cables are housed in the upper layer. The fibers leaving the splices are routed towards an outlet port of the upper layer.
The optical connection between a riser cable and one or more drop cables on a floor of the building can be housed in a junction box already installed on that floor. The branching device of U.S. Patent Publication No. 2010/0232752 can be used in this respect but has a number of disadvantages. First, because the splices between the fibers of the riser cable and the fibers of the drop cables—protected by the telescopic protection device—are housed within the duct that carries the drop cable, the telescopic protection device can become wedged within the duct. In addition, because the telescopic protection device is rather bulky, it is often possible to house only a single splice within each duct. Moreover, it is difficult to carry out maintenance on the riser cable or on the drop cable. What is more, maintenance has to be carried out gently on other cables present in the duct.
In contrast, the distribution box described by European Patent Publication No. 2,141,528 would allow both the splices and the excess length of the optical fibers to be housed in its interior. In particular, the dimensions and structure of the box are such as to allow about ten meters of optical fiber to be housed therein. However, this length of fibers is not necessary in FTTP or FTTH applications, and thus the distribution box of European Patent Publication No. 2,141,528 is needlessly complex and bulky. In addition, it is too bulky to be inserted inside a junction box.
Therefore, a need exists for an improved distribution box.